The present invention relates generally to paper handling apparatus and more particularly to a buffer mechanism used in a photofinishing system for conveying a cut sheet from one work station of the system operating at a first speed to a second workstation of the system operating at a faster speed.
In a photo finishing system of the type for which this invention relates, prints created by an ink jet printer are dried, cut into sheets that may include one or a number of prints, and then the sheets are laminated to protect the images. The lamination process is continuous in that the laminating material is applied to the cut sheets from a continuous roll of donor material. In order to minimize waste of the laminating material, it is desirable that the space between cut sheets be as small as possible. The desire for as small a space as possible between adjacent sheets is balanced against the need to prevent the leading edge of a following sheet from contacting the trailing edge of a leading sheet during the processing of the sheets. Accordingly, while it is necessary to maintain some gap or spacing between the cut sheets, this gap preferably is as small as possible.
The lamination process requires the application of heat and pressure to the sheets to effectively carry out the lamination process. Typically, this is done with lamination rollers that provide both the heat and pressure and this dual function makes the rollers somewhat bulky. The lamination process further requires that these rollers operate at an essentially constant speed and that the rollers operate continuously. It is important that the rollers not stop during the lamination process as this could destroy a sheet of prints.
From the laminator, the sheets may be fed to an embosser to provide the photographs with a desired matte finish. Like the laminator, the embosser uses relatively heavy rollers that carry out the embossing process by producing a textured surface on the laminate. The embosser rollers may be heated and need to operate continuously to produce a satisfactory surface. Also, the embossing process tends to proceed faster than the laminating process so there is a difference in the speed at which the laminating and embossing rollers operate. Thus, the problem exists of delivering the cut sheets from the laminator to an embosser operating at a faster speed.
The cut sheets emerging from the laminator may not be perfectly aligned when they are delivered to the embosser. Passing a skewed laminated sheet through the embosser will adversely effect the quality of the finished print. Accordingly, if the sheets are skewed leaving the laminator, it is necessary to realign or xe2x80x9cdeskewxe2x80x9d the sheets before delivering them to the embosser.
One method for deskewing is to provide a pair of transport rollers positioned to form a nip. If no corrective action is taken, a sheet of paper entering the nip at an angle will engage the rollers first at one point on the leading edge. The paper then will progressively enter the nip along the leading edge until the other side is reached so the sheet will pass through the nip in a skewed orientation. However, if the transport rollers are stopped the leading edge will butt against the nip and will align itself with the nip as the portion of the sheet immediately behind the leading edge forms a buckle or curled portion that takes up the skew. The transport rollers can then be energized to advance the now aligned sheet through the nip.
Stopping the transport rollers for a time sufficient to remove the skew at the leading edge of a first sheet causes the following sheet to close the gap between it and the trailing edge of the first sheet. Accordingly, the transport rollers must operate at a speed higher than a speed at which the cut sheets are delivered from the laminator or the buffer will fall behind, which is not acceptable.
As noted above, the operating speed of the embosser preferably is faster than the operating speed of the laminator. This arrangement allows the embosser to accept sheets from the transport roller without creating a backup. However, with the embossing process and laminating process operating at different speeds, the buffer must be long enough to accommodate the longest sheet being processed so that a sheet does not simultaneously engage the embosser rollers and the lamination rollers.
Accordingly, it is an object of this invention to provide a buffer for receiving cut sheets from a laminator in a photo finishing machine, exit the sheets, and delivering the sheets to an embosser.
Another object of this invention is to provide an apparatus and method for buffering sheets moving from one work station operating at a first speed to a second work station operating at a second, faster speed.
A further object of this invention to provide a buffer that accommodates the different operating speeds of the laminator and the embosser and provide an efficient transfer from one to the other while minimizing the gap between sheets.
While this invention is particularly well suited for the purpose just described, it will be understood that the nature of the processes that immediately precede and follow the buffer is not an element of the invention. The buffer can be used between any two processes where the requirements for receiving sheets for one process and delivering them to a second process are similar to those presented by the laminator and embosser described herein.
Briefly stated and in accordance with the presently preferred embodiment of the invention, a buffer of the present invention is disposed between a laminator and an embosser in a photo finishing machine. The buffer includes exit rollers forming a nip for receiving a leading edge of a cut sheet in a skewed orientation and registering the edge parallel to the rollers. Driven inlet rollers deliver the cut sheets to the exit rollers along a guide track at a speed equal to the output speed of the laminator.
A controller, operatively connected to the exit rollers and the inlet rollers, stops the exit rollers to allow the inlet rollers to move the leading edge of the cut sheet against the nip and form a slight buckle in the cut sheet. The controller then starts the exit rollers to advance the cut sheet partly through the exit roller and again stops the exit rollers. During all this time the inlet rollers continue to feed the cut sheet to the buffer from the laminator. Stopping the exit rollers prevents the possibility that the leading edge of the cut sheet will enter the embosser while the trailing edge of the sheet is still in the grip of the laminator or of the inlet rollers.
The guide track has a trap that opens on command from the controller so continued operation of the inlet rollers (while the exit rollers are stopped) forms a service loop of the cut sheet that extends through the open trap. In this fashion the buffer can accommodate a length of cut sheet that is longer than the guide track. A sensor signals the controller upon the passage of the trailing edge of the cut sheet past a fixed point. This indicates that the trailing edge of the cut sheet is free of the laminator. When this happens, the exit rollers are activated to turn at a faster speed that matches the operating speed of the embosser. The timing is such that the trailing edge of the cut sheet will clear the inlet rollers before the service loop is depleted so the cut sheet is not put into tension by rollers operating at different speeds.
As the trailing edge of the first sheet clears the inlet rollers, it drops away from the inlet rollers and through the open trap to create vertical clearance between the inlet rollers and the trailing edge. Due to the length of the service loop and the speed at which it is drawn by the exit rollers, it is possible that the leading edge of the following sheet entering between the inlet rollers will overtake the trailing edge of the first sheet. Keeping the trap open and creating the vertical clearance as noted above prevents the leading edge of the following sheet from contacting the trailing edge of the first sheet. The controller keeps the trap open until a gap between the first sheet and the following sheet is reestablished and then the trap is closed so the guide track can direct the leading edge of the following sheet to the exit rollers.
Accordingly, the present invention may be characterized in one aspect thereof by a buffer disposed between two workstations. The buffer receives cut sheets from a first work station operating at a first speed and delivers the cut sheets to a second work station operating at a second speed faster than the first speed. The buffer acts to maintain a separation or gap between the trailing edge of a first sheet and a leading edge of a following sheet and comprises:
a) inlet drive rollers for moving consecutive first and second spaced apart sheets into the buffer and in a forward direction along a path of travel to a buffer exit at a first sped;
b) exit inlet rollers for moving the sheets from the buffer at a second faster speed;
c) a controller operable to selectively stop the exit inlet rollers thereby stopping the forward progress of the first sheet while continuing to operate the inlet rollers such that a leading end of the second sheet overtakes a trailing end of the first sheet thereby eliminating the space between the sheets and creating an overlap of the sheets at some point in the buffer; and
d) the controller operable to drive the exit inlet rollers at the second faster speed to restore a spacing between the sheets and resolve the overlap prior to the leading end of the second sheet reaching the buffer exit.
In another aspect, the invention may be characterized by a method for buffering cut sheets moving from a first workstation operating at a first speed to a second workstation operation at a faster speed, the method comprising:
a) moving consecutive first and second spaced apart sheets from a first station and into a buffer inlet at a first speed, the sheets moving in a forward direction along a path of travel through the buffer to a buffer exit;
b) stopping the forward progress of the first sheet along the path of travel while continuing to move the second sheet at the first speed resulting in a leading end of the second sheet overtaking a trailing end of the first sheet thereby eliminating the space between the sheets and creating an overlap of the sheets at some point in the buffer; and
c) moving the first sheet through the buffer exit to a second station at a second faster speed and restoring a spacing between the sheets to resolve the overlap prior to the leading end of the second sheet reaching the buffer exit.